Through the mechanical properties experiments and analyses of ordinary marine concrete and marine concrete with fly ash added, it was thought that the proper content of SAP added could release free water for cement particles to continue hydrating during the curing stage, guarantee adequate water. So, SAP could significantly improve the performances of marine concrete. As to marine concrete with fly ash added, because part of fly ash took part in hydration process of cement particles and another part filled in gap structure of concrete, the appropriate content of SAP added was different from ordinary marine concrete and it should be according to the amount of fly ash added.